Hi!
Could you tell me which version(s) of Android do the phones have and which folder you're trying to access?
Viewing post in I cant import maps on android
The method you're describing to open the worldpack file directly with the game isn't supported.
To import packs, you'll first need to start the game and go to the "Packs" menu (which is on the right side of the room selection screen). From there you can tap on the "Import pack" button. That will open up a file picker which you can then use to find the pack and import it into the game.